Recently, with use of a small line photosensor (for example a CCD photosensor), highly condensed, two-dimensional data have become obtainable. Image data of an original are scanned by conducting light transmitted through or reflected at an original image to a line photosensor and varying the mutual positions of the original and the line photosensor in the subscanning direction (perpendicular to the lengthwise, or main scanning, direction of the line photosensor). Furthermore to record a color reproduction image, the three necessary data components, R (Red), G (Green) and B (Blue), have been conventionally obtained by either one of the following methods.
Japanese Patent Laid Open No. 56-58370, discloses a method by which original image three color component data are obtained by positioning successively three filters for R, G and B color components in front of a line photosensor when white light carrying the image data of the original is received by the line photosensor. The photosensor analyzes each scanning line three times for each color component as the original advances intermittently in the sub-scanning direction.
Japanese Patent Laid Open No. 56-16942 or 58-212255 discloses a method by which original image three color component data are obtained by time-sharing the switching of three lamps for R, G and B color components when light emitted from each lamp and carrying corresponding color component data of the original is received by a line photosensor. The photosensor also analyzes each scanning line three times for each color component as the original advances intermittently in the sub-scanning direction.
These methods have drawbacks in that the light quantity of each lamp is affected by voltage drift and by other factors over time, and further, that the effective light quantities for analyzing the color component data of R, G and B do not always agree with each other whether they are obtained by color component filters or by the individual lamps. Furthermore in the latter method, since the light intensities of the three lamps tend to vary individually owing to external or internal instabilities, total light quantities of the lamps within a given period are generally unequal.